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Also available are single spot lasers which are simply 
laser diodes that project a single spot to be measured. 
The user individually mounts and aims these lasers to 
measure discrete points on an object's surface. 
A dual-axis laser scanner unit is a stand-alone product 
that can be integrated under MNS control. The unit 
projects a single point beam of infrared laser light onto 
the object of interest. MNS measures the spatial coordi- 
nates of this point of diffusely reflected laser light. Contai- 
ned inside the unit are a laser source and two mirrors 
whose angular orientation are accurately controlled. The 
beam reflects off of these positioning mirrors, which direct 
the spot to the intended measurement location on the 
object. The "flying spot' scanner receives mirror positio- 
ning commands from MNS. The scanner also incor- 
porates a necessary laser beam autofocus function. 
2.4 CAD interface 
MNS is capable of relating the measurement data to the 
nominal CAD model of the particular object. This is 
performed through a Closest Point (normal to the surface) 
comparison of the physically measured data to its corres- 
ponding location on the nominal CAD surface. 
The data exchange with the CAD system is based on the 
use of the standard geometry data exchange format 
VDA-FS. The VDA-FS model is downloaded through an 
Ethernet link and stored locally in the MNS workstation. 
MNS then converts this VDA-FS model into a B-spline 
representation of the surface. 
During Closes Point measurements the CAD wire-frame 
appears in a window on the high resolution color monitor 
in a user-selectable orientation. Once a measurement is 
taken, the XYZ coordinate as well as its Closest Point to 
the nominal CAD reference is displayed numerically, and 
graphically on the CAD wire-frame. 
The Closest Point software can handle single point 
measurements (light pen applications) as well as simulta- 
neous measurement of multiple points (laser spot appli- 
cations). 
2.5 Six degrees of freedom software 
The Six Degrees of Freedom Software allows the user to 
measure the position and orientation of one object with 
respect to the position and orientation of another object, 
or any convenient Base Reference System. 
3 ACCURACY 
3.1 Resolution 
The sensor has a resolution very close to 0.01 pixel (10), 
due to a thorough optimization of signal to noise ratio as 
well as algorithms. 
In a camera setup covering a cubic measurement volume 
of 1.0 x 1.0 x 1.0 m?, and the two cameras set up to give 
optimum intersection angles, this corresponds to a spatial 
resolution of better than 40 um (U95 i.e. 20) all over the 
measurement volume. The resolution is better in the 
vertical direction due to redundancy. 
3.2 Absolute geometric accuracy 
The most important feature of the system is to obtain high 
geometric accuracy all over the measurement volume. 
The factory calibrated cameras, and the utilization of a 
certified reference bar to determine the exterior orientation 
of the cameras, ensures accurate and reliable results in 
any setup. 
The absolute accuracy is specified according to stan- 
dards used for conventional Coordinate Measurement 
Machines, e.g. the German norm VDI/VDE 2617. Accor- 
ding to this specification the accuracy of the system can 
be defined by the 'Uncertainty of Length Measurements' 
described by the formula: 
U,(3D)=0 .08+ [mm] 
Zn 
15000 
where L is the distance to be measured. This formula is 
based on light pen measurement, and means that what- 
ever position a reference length has in the measurement 
volume, its length will be determined within the specified 
accuracy with 95 % confidence. 
Further discussion of accuracy is given by Pettersen 
(1992). 
4 APPLICATIONS 
MNS is a general geometry measurement system dedica- 
ted for industrial applications. Its versatility and flexibility 
offers solutions to a large number of measurement 
problems: 
4.1 Quality Control of Stamped Parts (Off-line QC) 
Ref.: Saab Aircraft Division. 
One of the major applications of the Metrology Norway 
System is the measurement of manufactured surfaces, 
e.g. aircraft components made from composite materials 
or stamped automobile parts (fig. 3). After a die is 
changed on a stamping line, the first few parts off the 
stamping line are examined to quantify the deformations 
that exist in the part relative to its ideal shape (First- Off 
stamped part inspection). MNS is a fast and effective 
method in this application, eliminating the need for 
expensive reference fixtures. 
Applying the Light Pen for Closest Point measurements 
enable a very fast mapping of any deviations from the 
CAD model.